U.S. Pat. Nos. 7,389,644 and 7,406,828 disclose a CAES plants where a compressor supplies compressed air to an air storage during off-peak hours and, during peak hours, the stored compressed air is withdrawn from the storage, is preheated by utilizing the combustion turbine exhaust gas heat, and then is directed into an expander that generates the preheated compressed air power in addition to combustion turbine power. Conventional CAES plant operations are effective in achieving the prime goal of storing off-peak energy in the form of the compressed air and then using the preheated, stored compressed air for generation of the more needed and higher priced energy during peak hours, i.e., management of renewable and base power resources.
Still, electric grids require a number of additional very important functions such as grid regulation and emergency synchronous reserve. The grid regulation is easily provided by U.S. Pat. Nos. 7,389,644 and 7,406,828 that disclose CAES plants with practically instant load following operation of the CAES plants. The emergency synchronous reserve function requires very quick start-up and power delivery. The start-up time of the CAES plants described in each of U.S. Pat. Nos. 7,389,644 and 7,406,828, the contents of which are hereby incorporated by reference into this specification, is dependent on the startup time of combustion turbines (that can take approximately 20-30 minutes) to utilize the combustion turbine exhaust gas heat.
Thus, in a CAES system, there is a need to provide practically instant synchronous reserve power independent of the combustion turbine or other power generation structure.